N-terminally-truncated and modified amyloid-beta (A?) peptides are abundant in cerebral amyloid deposits in Alzheimer's disease (AD). Pyroglutamate A? is generated upon N-terminal truncation of A? followed by cyclization by glutaminyl cyclase to convert glutamic acid at residues 3 and 11 to pyroglutamate (A?pE3 and A?pE11). Both forms aggregate quickly, resist degradation, and are neurotoxic. It is unclear if either is present in initial A? deposition in plaques and blood vessels (i.e., acting as a seed for further deposition) or if they are modified later. However, Alzheimer's disease progression appears to correlate with the presence of A? pE peptide aggregates in brain. We hypothesize that pyroglutamate A? acts as a seed for A? deposition and accelerates inflammation, neurodegeneration and cognitive decline; therefore, targeted removal of this toxic species by immunotherapy will reduce A? deposition, inflammation and neuritic dystrophy, and protect against cognitive impairment without disturbing non-pathogenic A?. We propose 4 Specific Aims. Aim 1: We will determine if intrahippocampal or intraperitoneal injections of A?pE-containing mouse brain extracts enhance A? deposition, inflammation, neurodegeneration and cognitive decline in APP/PS1dE9 transgenic mice with aging in vivo. Aim 2: We will determine if early removal of pyroGlu A? prevents general A? plaque deposition and neuritic changes, and protects against cognitive decline by passively immunizing (i.p.) male APP/PS1dE9 tg mice with an anti-A?N3pE mAb (07/1), an anti-A?pE11 mAb, a general A? mAb (3A1), or PBS weekly from 4-12 mo of age, starting prior to plaque onset. Outcome measures: behavioral, biochemical, and neuropathological analyses. Aim 3: We will determine if removal of pyroGlu A? in late stage AD reduces total A? and neurodegeneration and improves cognitive deficits by passively immunizing (i.p.) female APP/PS1dE9 tg mice weekly from 12-16 mo of age, starting well after plaque onset. Antibodies and outcome measures are the same as in Aim 2. Aim 4: We will examine the immune response of microglia to pyroGlu A? mAbs in acute in vivo studies and in primary microglial cultures in vitro. Our collaborators at Probiodrug AG (Germany) will kindly provide us with 2 high-affinity, highly selective pyroGlu A? mAbs (anti- A? pE3 and anti-A?pE11), synthetic A?pE peptides, and brain extracts from their transgenic mouse models that accumulate pyroGlu-3 A? peptides. Our collaborators at the CND have generously provided the 3A1 general A? mAb hybridoma as a control. Importantly, my lab initiated this collaboration and has many years of experience investigating pyroGlu A? deposition, inflammation, and A? immunotherapy. The overall goal of our study is to determine whether pyroglutamate A? proteins (A?pE3 and A?pE11) are therapeutic targets for Alzheimer's disease and, whether clearance by immunotherapy specific for either pyroGlu A? species would be efficacious to prevent and/or treat AD.